Thanks!
Regardless of one's opinion about motional or positional feedback applied to a sub, both suffer from the limitations of the accelerometer used, the second voice coil being 'read'. Both are transducers, thus with their own dynamic range limitations, frequency response, resonances, distortions.
Also, the sensor often cannot not pick up motion from more than one direction/dimension- it can't see the cone "rocking" very well, for example- it only sees that it has not stroked far enough. However, a 1-D sensor is cheaper. And marketable. It can help a poor woofer or bad box design.
It's far better to design the best possible woofer and put it into a proper cabinet (not easy), and get the phase accuracy of the electronic crossover correct, by choosing certain slopes of the filters:
Use a 24dB/octave slope on a sub and 12dB/octave on the speakers, if they are sealed or ported, and if the sub is not a resonant bandpass design (THX markets this standard pro-sound crossover as something unique). The crossover point belongs near the impedance peak of the sealed box, or near the upper impedance peak of a ported box.
Other option: If they are panel speakers/Quads- don't give them a crossover. Just put 6dB/octave electrically onto the subs only (must be stereo subs for this).
Either way, you get better phase alignment all through the crossover range- which SOUNDS LIKE far less room problems.
To fine tune either: listen with the sub at the same tape-measure distance from your ear as the main speakers' woofer centers. Then move the sub +/- 12" front-to-rear off that plane/arc. As you do so, listen for dynamics and then for tonal uniformity (separate tests).
Listen to something steadily percussive at the crossover point- a kick drum for 50Hz, a floor-tom drum at 80Hz. You will hear the best dynamic "alignment" as you change front-to-rear position and fuss (a little bit) with the crossover point.
Then listen to a string bass run the scale- try Christian McBride on his "Gettin' To It" album, or use a celloist's solo. This lets you find general tonal weaknesses/boosts most easily. Changing the crossover point may not help much, but try. Usually if there is a drop/boost in output in a range of frequencies, that's the room, as that is how rooms behave on music. To address this, pick up the entire speaker, sub and chair layout, and move it out further into the room by 18 inches and hear what happens. Don't touch the volume control or crossover settings- one variable at a time.
Your question about "proper" digital correction:
Walk around a speaker and ask what sort of things need correcting? Can you point to them?
Do we wish to correct digitally for cone breakup? But that breakup "nature" varies with the music's dynamics and tonal spectrum, and that we cannot measure with a test tone!
Do we wish to correct for a floor reflection? That is heard differently by ours ears than by the mic, so the mic's signal is not "accurate"- hence the LF cutoffs of digital correction. This explains a little of the higher crossover point choice: it narrows dispersion and thus reduces cabinet and floor reflections in that higher tone range.
Is it a "splash" reflection of many simultaneous tones, coming off a big, curved front face? If so, ask what is the 1/4-wave dimension of the panel? Because from that tone on up, you get the "splash"- a new bubble of sound launched off the face- and that happens all the way right down next to the dome of the tweeter. This is what the digital units try most to correct for in the direction of your chair only. But that leaves many driver non-linearites uncorrected, as to the mic, those were swamped by the splash. The mic cannot separate them from the splash the way our ears can.
With digital correction, what is going to happen to the sound everywhere else in the room? Not just what others would hear, but what will be coming back to my chair from the walls? Whatever that is, it can't be zero. And it's definitely not "corrected".
One has to ask ALL the right questions of the digital correction situation. Make the speakers better in the first place is my answer. Costs less, sounds better. Then try correction.
As far as placing the speakers out into the room? Yes, if they were designed from scratch for that location. You cannot have it both ways- i.e., a speaker design accurate when placed within a few feet of the wall, vs. many feet out. As that distance from the back wall is varied, the perceived output below 300Hz changes, unless the speaker is the size of a `fridge. This cannot be balanced out with a switch on the back of the speaker. And in my opinion, it cannot be corrected properly by digital means.
Actually, it's not my opinion, but what physics says we are still going to hear come off that back wall (even with digital correction). To any speaker designer, the first question after, "What kind of room do we have to work in?" is, "How far out from the walls can most users live with these speakers, so they can actually hear the depth of the image?" The third question is always, "How high up the scale is the woofer to go?"
There IS a distance from the back wall which is "far enough"- the Hass effect is an indicator of that distance.
Sorry I could not respond sooner- too much work. Website coming soon.
Best regards,
Roy
Green Mountain Audio
A side note: Anyone recommending a really wide-set speaker placement is throwing a bigger acoustic shadow on your opposite ear. Why do that? When they are set up in the normal 48-53 degree spread (the limits of our peripheral vision by the way), their image is unstable as you turn your head- usually because of double drivers, multiple drivers, or line sources.
As you turn your head, there remains a constant acoustic field UNDER YOUR CHIN, because you have a chest making lots of nearfield reflections. But for sound coming over the top of your head, the field is determined only by the direct sound from the speakers. And if there is sound being launched from higher than your head and also from the same height simultaneously, then the opposite ear hears more of the "higher" driver location as you turn- and the image jumps to that speaker. If the source of the sound is more compact than your head, the image does not jump.
Listen to a solo voice with your eyes closed, no eyeglasses, no coffee table in front of you, nor footstool, in a very quiet room, to identify any image jump most easily.
Regardless of one's opinion about motional or positional feedback applied to a sub, both suffer from the limitations of the accelerometer used, the second voice coil being 'read'. Both are transducers, thus with their own dynamic range limitations, frequency response, resonances, distortions.
Also, the sensor often cannot not pick up motion from more than one direction/dimension- it can't see the cone "rocking" very well, for example- it only sees that it has not stroked far enough. However, a 1-D sensor is cheaper. And marketable. It can help a poor woofer or bad box design.
It's far better to design the best possible woofer and put it into a proper cabinet (not easy), and get the phase accuracy of the electronic crossover correct, by choosing certain slopes of the filters:
Use a 24dB/octave slope on a sub and 12dB/octave on the speakers, if they are sealed or ported, and if the sub is not a resonant bandpass design (THX markets this standard pro-sound crossover as something unique). The crossover point belongs near the impedance peak of the sealed box, or near the upper impedance peak of a ported box.
Other option: If they are panel speakers/Quads- don't give them a crossover. Just put 6dB/octave electrically onto the subs only (must be stereo subs for this).
Either way, you get better phase alignment all through the crossover range- which SOUNDS LIKE far less room problems.
To fine tune either: listen with the sub at the same tape-measure distance from your ear as the main speakers' woofer centers. Then move the sub +/- 12" front-to-rear off that plane/arc. As you do so, listen for dynamics and then for tonal uniformity (separate tests).
Listen to something steadily percussive at the crossover point- a kick drum for 50Hz, a floor-tom drum at 80Hz. You will hear the best dynamic "alignment" as you change front-to-rear position and fuss (a little bit) with the crossover point.
Then listen to a string bass run the scale- try Christian McBride on his "Gettin' To It" album, or use a celloist's solo. This lets you find general tonal weaknesses/boosts most easily. Changing the crossover point may not help much, but try. Usually if there is a drop/boost in output in a range of frequencies, that's the room, as that is how rooms behave on music. To address this, pick up the entire speaker, sub and chair layout, and move it out further into the room by 18 inches and hear what happens. Don't touch the volume control or crossover settings- one variable at a time.
Your question about "proper" digital correction:
Walk around a speaker and ask what sort of things need correcting? Can you point to them?
Do we wish to correct digitally for cone breakup? But that breakup "nature" varies with the music's dynamics and tonal spectrum, and that we cannot measure with a test tone!
Do we wish to correct for a floor reflection? That is heard differently by ours ears than by the mic, so the mic's signal is not "accurate"- hence the LF cutoffs of digital correction. This explains a little of the higher crossover point choice: it narrows dispersion and thus reduces cabinet and floor reflections in that higher tone range.
Is it a "splash" reflection of many simultaneous tones, coming off a big, curved front face? If so, ask what is the 1/4-wave dimension of the panel? Because from that tone on up, you get the "splash"- a new bubble of sound launched off the face- and that happens all the way right down next to the dome of the tweeter. This is what the digital units try most to correct for in the direction of your chair only. But that leaves many driver non-linearites uncorrected, as to the mic, those were swamped by the splash. The mic cannot separate them from the splash the way our ears can.
With digital correction, what is going to happen to the sound everywhere else in the room? Not just what others would hear, but what will be coming back to my chair from the walls? Whatever that is, it can't be zero. And it's definitely not "corrected".
One has to ask ALL the right questions of the digital correction situation. Make the speakers better in the first place is my answer. Costs less, sounds better. Then try correction.
As far as placing the speakers out into the room? Yes, if they were designed from scratch for that location. You cannot have it both ways- i.e., a speaker design accurate when placed within a few feet of the wall, vs. many feet out. As that distance from the back wall is varied, the perceived output below 300Hz changes, unless the speaker is the size of a `fridge. This cannot be balanced out with a switch on the back of the speaker. And in my opinion, it cannot be corrected properly by digital means.
Actually, it's not my opinion, but what physics says we are still going to hear come off that back wall (even with digital correction). To any speaker designer, the first question after, "What kind of room do we have to work in?" is, "How far out from the walls can most users live with these speakers, so they can actually hear the depth of the image?" The third question is always, "How high up the scale is the woofer to go?"
There IS a distance from the back wall which is "far enough"- the Hass effect is an indicator of that distance.
Sorry I could not respond sooner- too much work. Website coming soon.
Best regards,
Roy
Green Mountain Audio
A side note: Anyone recommending a really wide-set speaker placement is throwing a bigger acoustic shadow on your opposite ear. Why do that? When they are set up in the normal 48-53 degree spread (the limits of our peripheral vision by the way), their image is unstable as you turn your head- usually because of double drivers, multiple drivers, or line sources.
As you turn your head, there remains a constant acoustic field UNDER YOUR CHIN, because you have a chest making lots of nearfield reflections. But for sound coming over the top of your head, the field is determined only by the direct sound from the speakers. And if there is sound being launched from higher than your head and also from the same height simultaneously, then the opposite ear hears more of the "higher" driver location as you turn- and the image jumps to that speaker. If the source of the sound is more compact than your head, the image does not jump.
Listen to a solo voice with your eyes closed, no eyeglasses, no coffee table in front of you, nor footstool, in a very quiet room, to identify any image jump most easily.